The present invention relates to an agitator ball mill in accordance with the independent claim.
An agitator ball mill of the generic kind is describedrein comprises a substantially cylindrical grinding chamber which is, for example, in WO 2010/112274. The agitator ball mill described the bounded by a cylindrical wall and by an inlet-side end wall and an outlet-side end wall, and a rotatably mounted agitator shaft on which paddle-wheel-like agitator elements, also referred to as accelerators, are arranged spaced apart from one another axially inside the grinding chamber. In the vicinity of the inlet-side end wall there is arranged an inlet for supplying material to be ground and grinding bodies and in the outlet-side end wall there is provided an outlet for removal of the ground material, which outlet is separated from the grinding chamber by a separator screen that holds back grinding bodies. During operation, the agitator shaft and accordingly the agitator elements that are joined thereto for conjoint rotation therewith are set in rotation by an external motor. Agitator ball mills of similar construction are described, for example, in EP 0 627 262 and EP 2 272 591.
During the grinding and/or dispersing process, those agitator ball mills which are provided with paddle-wheel-like agitator elements convey a portion of the mixture formed from grinding bodies and the material being ground and/or dispersed radially outwards, whereupon at least a portion of the mixture flows in the direction of the agitator shaft and is thence sucked back into the conveyor chambers of the agitator elements. That process is referred to hereinbelow as the grinding body cycle.
In known agitator ball mills of that type, in certain configurations the problem arises that during the grinding or dispersing process only an insufficient portion of the radially outwardly conveyed mixture formed from grinding bodies and the material being ground and/or dispersed flows in the direction of the agitator shaft and is thence sucked back into the conveyor channels of the agitator elements. This occurs particularly when the kinetic energy of the grinding bodies is so great that their inertial forces are greater than the tractive forces of the material being ground and/or dispersed. In that case a separation takes place between grinding bodies and the material being ground and/or dispersed, that is to say the material being ground and/or dispersed is caught up by the intended grinding body cycle while the majority of the grinding bodies become compacted towards the periphery of the grinding chamber. This can have the result, firstly, that product flowing subsequently into the grinding chamber collects on the compacted grinding bodies and, as a result, the pressure in the grinding chamber initially rises until the layer of grinding bodies breaks open locally under the effect of the compressive forces and the pressure then spontaneously falls again. This can lead to vibrations in the agitator ball mill. A further possible consequence of the accumulation of grinding bodies towards the periphery of the grinding chamber is a sub-optimum grinding result.